No Sound from NAD 7240PE

[mbz]

but not good at R312 (-19 and 60mv).

Sorry, I missed that point, means high current through R312, caused by opamp short. Need to
replace the opamp IC301 (NJM2043)

Another possibility is C312 (100uf/25V) is leaking. Suggest replace that first. Also check
for dry solder joints at R312, IC301 pin 4. Might be lucky it's just the cap...

 

[craigsc]

Thanks, I replaced c312 and the other caps in the circuit with no luck. I’ll check the solder and l ordered a NJM2043. Will try that next.

 

[mbz]

To be honest, I'm not real happy that one side of R312 is in spec (-19V) but the other side is almost zero (60mV) (negative?)
If there was such a current drain then would expect the supply voltage to be down a little, reason for looking at solder joints.
If the IC at fault then would expect it to be warm to touch (after power off/unplug) or temp sensor better still. Certainly put in
a DIP(?) socket for future changes if needed.

 

[craigsc]

Reflowed the IC with no effect. It is -60mv on the other side. I think I'll pull Q502 and check that to confirm the power supply is good.

 

[craigsc]

replaced the opamp with no change. Also pulled and replaced Q502 with no change. Any one have any other ideas where the drain is? Seems like it must be a short somewhere.

 

[craigsc]

So after some analysis, I decided to pull the caps in the 20v power supply for the opamp, C515, C516, C517, and C518. Turns out all of these 47uf/25v caps were in bad shape. Replaced with some 47uf/35v and everything works. A solid -19v/-14.5v on R312 and both channels working after some serious deoxiting of the volume pot!! Thanks for the help folks.